CHARACTERIZING CHANGES IN AGGREGATE STABILITY SUBSEQUENT TO INTRODUCTION OF FORAGES

Limited information exists on the methods used to compute the changes in wet aggregate stability, WAS, with time subsequent to changes in ma nagement practices. The objectives of this study were to: (i) develop a model to compute the net gain in WAS, WAS(net), with time subsequent to the introduction of forages, (ii) assess the model using data from different soils, and (iii) determine the influence of soil properties on the regeneration of WAS. Stability measurements were made at month ly intervals during the 1989, 1990, and 1991 growing seasons from seve n different soils under continuous conventional corn (Zea mays L.) and forage treatments established in 1989. The interaction of cropping tr eatment, time of sampling, and gravimetric soil water content, theta, at sampling was significant for six out of seven soils at P = 0.05. Us ing the relation between WAS and theta and the changes in WAS with tim e, a semiempirical model was developed to predict WAS(net). The model parameters described (i) the duration of delay before any observable c hanges in WAS occurred, (ii) the rate at which WAS increased from an i nitial to a maximum value, and (iii) the maximum potential change in W AS. The R2 for the best fit of the model ranged from 0.31 to 0.72 for the seven soils. The projected half-life for WAS(net), computed using the 3-yr data, ranged from 4.52 yr for a clay loam to 7.75 yr for a sa ndy loam. Pedotransfer function analysis indicated that WAS(net) incre ased with increasing clay and organic matter contents and pH of soil. The model parameters and the associated pedotransfer functions were us eful in assessing the influence of soil properties on stability follow ing changes in management practices.